Many applications require sufficient multichannel reception of signals. Search for signals could easily be accomplished by series of Fourier Platforms, but its time and frequency resolution is insufficient to demodulate found signals effectively. Using narrowband signals is one of simplest ways to improve efficiency and reliability of transmission, but it is limited by carrier frequency uncertainty resulting in carrier frequency offset in receiver. In most systems, carrier frequency must be relatively low compared to signal bandwidth.
In some prior art solutions, signal bandwidth is increased, and noise tolerance is managed using some sort of error-correction coding of just repetitions. For example, LoRa wireless protocol is widely known. It uses chirp spread spectrum, utilizing very wide bands compared to information speed of transmission. LoRa uses CDMA multiple access, which is different from the solution proposed in the present invention.
SigFox is another prior art solution employing multichannel receivers with carrier tracking. This solution is limited by computational inefficiency of carrier tracking systems. Also, it is algorithmically and computationally difficult to employ error correction coding in such systems, as they are limited by noise tolerance of carrier tracking systems. So, some sort of code-aided tracking might be necessary, which may be further complicating such solutions.
The present invention solves two main problems related to wireless communications: receiving many simultaneous messages and receiving narrowband messages with frequency offset greater than signal bandwidth. These problems are common for many m2m and Low-Power Wide Area Network (LPWAN) communication systems. LPWAN systems must transmit and receive many signals simultaneously and efficiently.